OneWay Databinding for ViewModel - asp.net-mvc

Question

I have some fields in my ViewModel that I only need for the output in my View. But they are always getting send when submitting the form. That's not only annoying, but also dangerous, because I definitly don't want that databinding for these viewmodel fields.
Are there any change to define a OneWay Databinding for some of my viewmodel properties?
Thx in advance
EDIT:
The problem ist, that the Pictures and ValidSizes List is send back to the server when I click to an ActionLink.
http://localhost:52176/?PageSize=30&Index=31&Pictures=System.Collections.Generic.List%601[System.String]&Size=100&ValidSizes=System.Collections.Generic.List%601[System.Web.Mvc.SelectListItem]
public class PicturesViewModel
{
public const int SMALL = 100;
public const int MIDDLE = 150;
public const int BIG = 250;
public int PageSize { get; set; }
/// <summary>
/// Initializes a new instance of the <see cref="PicturesViewModel"/> class.
/// </summary>
public PicturesViewModel()
{
Pictures = new List<string>();
Size = SMALL;
Index = 1;
PageSize = 30;
}
/// <summary> Gets or sets the index. </summary>
public int Index { get; set; }
/// <summary>
/// Gets or sets the picture links.
/// </summary>
/// <value>The picture links.</value>
public List<string> Pictures { get; private set; }
/// <summary>
/// Gets or sets the size.
/// </summary>
/// <value>The size.</value>
public int Size { get; set; }
private List<SelectListItem> validSizes = null;
/// <summary>
/// Gets the valid sizes.
/// </summary>
/// <value>The valid sizes.</value>
public IEnumerable<SelectListItem> ValidSizes
{
get {
if (validSizes != null)
return validSizes;
validSizes = new List<SelectListItem>
{
new SelectListItem(){Text = "Small", Value = SMALL.ToString()},
new SelectListItem(){Text = "Middle", Value = MIDDLE.ToString()},
new SelectListItem(){Text = "Big", Value = BIG.ToString()}
};
return validSizes;
}
}
}
EDIT2:
<div id="pager_left">
<%= Html.ActionLink("Prev", "Prev", Model)%>
</div></td>
That's the Action Link that causes the binding.

Answer 1

Use separate ViewModel for form input
Use IEnumerable instead of List
Use [Bind(Exclude="Pictures, ValidSizes")] on the action input parameter
Use private setters
Don't create form input elements for Pictures/ValidSizes if you don't need them
and so on.
Update:
You assign different ViewModel not to a view, but to the controller action that handles link click. And from your questions it seems that what you need is not "oneway" binding, but rather avoiding extra characters in URL - because, if your ValidSizes is IEnumerable it won't be altered, and anyway in your URL its data is wrong, won't cause update - so it's already "one-way" binding.
This is what I can find for your problem:
http://forums.asp.net/t/1328683.aspx
As for solution, I never use ActionLink helper myself, because it is a leaky abstraction and I don't like to fight with it. Simple html link tag is always much better.
<a href="<%= Html.BuildUrlFromExpression<>() %>" />
I actually use my own few-lines version of the BuildUrlFromExpression for this. Also see in the link above how you can pass parameters via anonymous object instead of Model (new { PageSize = Model.PageSize, index = Model.index }).